This invention relates to the use of organometallic salts for pigment management in microporous inkjet receptor media.
Inkjet imaging techniques have become vastly popular in commercial and consumer applications. The ability to use a personal computer and desktop printer to print a color image on paper or other receptor media has extended from dye-based inks to pigment-based inks. The latter provide brilliant colors and more durable images because pigment particles are contained in a dispersion before being dispensed using a thermal inkjet print head, such as those commercially available from Hewlett Packard Corporation or LexMark Corporation in inkjet printers commercially available from Hewlett Packard Corporation, Encad Inc., Mimaki Corporation, and others.
Ink jet printers have been in general use for wide-format electronic printing for applications such as, engineering and architectural drawings. Because of the simplicity of operation, economy of ink jet printers, and improvements in ink technology the inkjet imaging process holds a superior growth potential promise for the printing industry to produce wide format, image on demand, presentation quality durable graphics.
The components of an ink jet system used for making graphics can be grouped into three major categories:
1 Computer, software, printer.
2 Ink.
3 Receptor sheet.
The computer, software, and printer will control the size, number and placement of the ink droplets and will transport the receptor film. The ink will contain the colorant or pigments which form the image and the receptor film provides the medium which accepts and holds the ink. The quality of the ink jet image is a function of the total system. However, the composition and interaction between the ink and receptor film is most important in an ink jet system.
Image quality is what the viewing public and paying customers will want and demand to see. Many other demands are also placed on the ink jet media/ink system from the print shop, such as rapid drying, humidity insensitivity, extended shelf life, waterfastness and overall handleability. Also, exposure to the environment can place additional demands on the media and ink (depending on the application of the graphic).
Porous membrane is a natural choice to use as an ink jet receptive media because the capillary action of the porous membrane can wick the ink into the pores much faster than the absorption mechanism of film forming water soluble coatings. However, in the past, when a porous coating or film has been employed to achieve desired quick dry, optical density has suffered greatly because the colorant penetrates too deep into the porous network. This type of problem is magnified by printers that dispense high volumes of ink per drop because extra film thickness may be required to hold all the ink. When the pore size and pore volume of the membrane are opened to allow the pigments to penetrate, the pigments can be stratified in the membrane. Meaning, the black, cyan, magenta, and yellow will be predominately found at different depths depending on the order of application. Hence, some of the first color(s) applied is/are optically trapped in the image by subsequent application of other pigmented ink. Furthermore, lateral diffusion of the ink can also be a problem inherent in porous membranes used as receptive media. When pigmented inks are jetted onto a porous film that has a pore size that is too small, color pigments will be filtered on the top of the membrane rendering high image density, but the pigments could easily smear and have the effect of never drying. Also, excess fluid from the ink can coalesce, or even worse, pool and run on the image before the water/glycol carrier is wicked away.
The chemical formulation of the pigmented inkjet ink has considerable complexity due to the requirement of continued dispersion of the pigment particles in the remainder of the ink and during jetting of the ink.
The typical consumer medium for receiving dye-based inkjet inks has been paper or specially coated papers. However, with too much inkjet ink in a given area of the paper, one can see the over-saturation of the paper with the aqueous ink in which dye was dissolved.
As inkjet inks have become more commercially oriented and pigmented-based inks have become more prevalent, different media have been tried in an attempt to control the management of fluids in the ink.
Japanese Patent JP 61-041585 discloses a method for producing printing material using a ratio of PVA/PVP. The disadvantage is inadequate waterfastness and wet rub off properties.
Japanese Patent JP61-261089 discloses a transparent material with cationic conductive resin in addition to a mixture of PVA/PVP. The material is water fast and smudge proof but the wet rub off properties are poor.
European Patent Publication EP 0 716 931 A1 discloses a system using a dye capable of co-ordinate bonding with a metal ion in two or more positions. Again binder resins are used with inorganic pigments in the paper or film. The metal ion was preferred to be jetted on before imaging and additional heating is necessary to complete the reaction. This system was not claiming to be water fast; the focus was long term storage without fading from heat or light.
U.S. Pat. No. 5,537,137 discloses a system to achieve waterfastness by curing with heat or UV light. In the body of the patent, examples of their coatings contained Ca++ from CaCl2. This was added to provide reactive species for the acid groups on the dispersed polymer. The coating remains water soluble until UV or heat curing after imaging.
Hence, the current special ink jet media employ vehicle absorptive components, and sometimes optional additives to bind the inks to the media. As a consequence current media are inherently moisture sensitive and can be fragile to handling and subject to finger smearing. Moreover, the vehicle absorptive components usually consist of water soluble (or swelling) polymers which result in slower printing speeds and dry times.
Pigmented ink delivery systems have also dealt with pigment management systems, wherein the resting location of the pigment particles are managed to provide the best possible image graphic. For example, copending, coassigned, U.S. Pat. No. 5,747,148 (Warner et al.), discloses a pigment management system in which a suitable supporting layer (including in a listing a microporous layer) has a two layer fluid management system: a protective penetrant layer and a receptor layer, both layers containing filler particles to provide two different types of protrusions from the uppermost protective penetrant layer. Electron microphotographs in that application show how the pigment particles of the ink encounter smooth protrusions that provide a suitable topography for pigment particle xe2x80x9cnestingxe2x80x9d and rocky protrusions that assist in media handling and the like.
Other ink receptors have been disclosed, including U.S. Pat. Nos. 5,342,688 (Kitchin); 5,389,723 and 4,935,307 (both Iqbal et al.); 5,208,092 (Iqbal) 5,302,437 (Idei et al); U.S. Pat. No. 5,206,071 (Atherton et al.); and EPO Patent Publication 0 484 016 A1.
One prior activity has combined a fluid management system with a pigment management system, as disclosed in copending, coassigned, U.S. patent application Ser. No. 08/892,902 now U.S. Pat. No. 6,632,510, the disclosure of which is incorporated herein by reference. The work concerns the use of multivalent metal salts which in aqueous solution releases metal ions and an inorganic anion. Whereas the metal ion plays the role of pigment management system the metal anion does not play any role in the composition except being a cationic partner.
In the present work, an organometallic salt improves on the art by rapidly releasing multivalent metal cation which takes care of the pigment management function and an organic anion which provides useful organic acid to control smudgeness and drying of the film. This work, therefore, solves the need for an inkjet receptor to have both a pigment management system for flocculating or agglomerating of incoming ink and a drying agent for the humectants of the ink thus efficiently drying the pigmented inks within a porous substrate.
One aspect of the invention is an inkjet receptor medium, comprising a composition of matter comprised of an organometallic salt of a multivalent metal cation and an organic acid anion.
One aspect of the present invention is to provide a metal salt that releases a metal cation for pigment management and simultaneously releases an organic acid anion of a carboxylic or sulfocarboxylic or phenolic acid or hydroxy or mixed functionalities thereof to take care of the drying aspect of the ink system. xe2x80x9cDrying agentxe2x80x9d means an agent, component, ingredient or compound which can dry or make the pigment feel dry to touch via chemically or physicochemically occlusion or interaction with certain components such as the humectant or other slow drying components in the pigmented inks used in printing the image onto the receptor medium. Specifically, xe2x80x9cdry to touchxe2x80x9d means, an indistinguishable xe2x80x9cfeelxe2x80x9d between the imaged and the unimaged areas of the substrate regardless of whether, technically, all volatiles have evaporated from the imaged area.
One feature of the present invention is a multivalent organometallic salt that releases a multivalent metal ion for pigment management and an anion of an organic acid consisting of a carboxylic and/or a sulfonic acid or hydroxyl or a phenolic or a mixed functionality thereof in a composition in an aqueous solution wherein the acid works as an ink-drying agent in a film coated with the said composition.
One advantage of the present invention is that both the multivalent metal cation and the organic acid can be derived from the same salt/component. This advantage avoids the necessity of providing two different components to a porous substrate. Furthermore, the procedure minimizes the possibility that the coating solutions become contaminated with any undesirable residue or components or by product-compounds as contaminants.
Another feature of the present invention is that a composition including the organometallic salt, surfactant and the migration inhibitor uses a lesser amount of total solids to achieve comparable performance. Thus, one can minimize concentration to obtain equivalent performance or maximize concentration to achieve previously-unattainable performance.
Other features and advantages of the invention will be disclosed in relation to the embodiments of the invention.
Inkjet Receptor Medium
The inkjet receptor medium can be any porous membrane or film known to those skilled in the art wherein it is desired to print inkjet inks on at least one major surface thereon. Preferably, the medium comprises an inkjet receptor medium, comprising a porous substrate having a fluid management system and having a pigment management system in contact with surfaces of pores of the substrate therein, such as disclosed in copending, coassigned, U.S. patent application Ser. No.08/892,902 now U.S. Pat. No. 6,632,510, the disclosure of which is incorporated herein. The pigment management system includes a multivalent metal salt coating or functionalized particulates impregnated in pores of the porous substrate such that they are in contact with surfaces of pores of the porous substrate. One embodiment of that medium is an inkjet receptor comprising a microporous membrane impregnated with an multivalent metal salt together with a surfactant or combination of surfactants chosen for the ink and membrane being employed.
Another embodiment is an inkjet receptor comprising a microporous membrane impregnated with a microporous fluorinated silica agglomerate together with a binder and a surfactant or a combination of surfactants for the ink and membrane being employed.
Another embodiment of that medium is an inkjet receptor comprising a microporous membrane impregnated with a microporous fluorinated silica agglomerate together with a binder and a surfactant or combination of surfactants wherein the surfactants are selected from the group of hydrocarbon-based anionic surfactants, silicon-based non-ionic surfactants or fluorocarbon-based non-ionic based surfactants or a combination thereof.
These receptors, when imaged in an inkjet printer, provide very high density and very high quality images which are tack-free and instantaneously dry to touch.
One embodiment of the present invention is an inkjet receptor comprising a microporous membrane impregnated with an organometallic multivalent salt together with a hydrophilic surfactant and an optional migration inhibitor polymer/copolymer chosen from a series of hydrophilic/hydrophobic polymers/copolymers.
Another embodiment of the present invention is an inkjet medium comprising a microporous membrane impregnated with an organometallic multivalent salt wherein the said salts are derived from various aromatic acids consisting of sulfonic, carboxylic, phenolic, hydroxyl and mixed functionalities thereof and wherein the metal ions may be derived from group IIA to VIA and more preferably from group IB to VIIIB in the Periodic Table. Specific examples, include, but are not limited to, Al, Mg, Zn, Fe, Bi, Ga, Sn, Ca, Ti, Zr, Cu, Co etc.
Nonlimiting examples of organometallic salts useful in the present invention include:.
Metal Sulfocarbolates 
Metal Hydroquinonesulfonates 
Metal dihydroxybenzenedisulfonates 
Metal Sulfosalicylates 
Metal Sulfophthalates 
Metal Carboxylates 
Metal Calix(n) Arene Sulfonates 
Another embodiment of the present invention is an inkjet medium comprising a microporous membrane impregnated with an organometallic multivalent salt wherein the salt releases both a multivalent metal cation and an organic acid anion and wherein the metal cation plays the role of pigment management system and the organic acid anion plays the role of a dehydrating or drying agent thus making the image in the membrane smudge-free to touch.
Another embodiment of the present invention is an inkjet medium comprising a microporous membrane impregnated with an organometallic multivalent salt wherein the salt releases both a multivalent metal cation and an organic acid anionxe2x80x94both simultaneously being useful for pigment management system and humectant management system in the ink.
Another embodiment of the present invention is an inkjet coating composition that incorporates an organometallic multivalent salt with a surfactant and a binder only to give a composition which provides 0.33 to 0.25 of the coating weight of that a composition consisting of a metal salt, a surfactant, organic acid and a binder, such as that disclosed in the copending, coassigned U.S. patent application Ser. No 08/892,902 (Waller et al.), now U.S. Pat. No. 6,632,510, which discloses a fluid management system in combination with a pigment management system and which is incorporated by reference as if rewritten herein.
The ink colorant is typically a pigment dispersion having a dispersant that binds to the pigment and that will destabilize, flocculate, agglomerate, or coagulate the pigments on contact with the media component. Depositing each of the colors at or just below the surface of the membrane allowing the carrier fluid to wick into the membrane where the fluid management system can take over while providing a sheltered location for the pigments as managed by the pigment management system.
Porous substrates useful in the present invention include symmetrical membranes, asymmetrical membranes, and porous films also known as skinned membranes. Symmetrical membranes have porosity on opposing major surfaces of approximately the same pore size. Asymmetrical membranes have porosity on opposing major surfaces that are not of similar pore sizes. A skinned membrane has considerable porosity on one major surface but essentially no porosity on the opposing major surfaces.
Nonlimiting examples of commercially available microporous membranes include: nylon and polysulfone membranes from Gelman Sciences, Ann Arbor Mich.; polyolefin membranes from Amoco Corp., Chicago Ill.; and polyolefin, nylon, or ethylene vinyl alcohol membranes from 3M.
A suitable microporous membrane for printing on a 100-140 picoliter per drop size for each color and 300xc3x97300 drops per inch printer has a thickness or caliper ranging from about 75 xcexcm to about 200 xcexcm, and preferably from about 100 xcexcm to about 175 xcexcm It is a reality of ink jet printing that as many as four pigment drops, representing each of the four printing colors, are landing on a single spot of the ink jet receptor medium in order to generate any one of the myriad of colors available in ink jet printing.
The microporous membrane can have a porosity value as calculated by measuring the bulk density of the membrane in grams/cm3 from the specific gravity measurement determined according to ASTM-D-792-66 and substituting that value into the following formula:
100xc3x97[1-measured density/polymer density]=porosity,
ranging from 20 to about 95 and preferably from about 30 to about 50. Alternatively, the membrane can have a pore volume ranging from about 80 to about 100% of the anticipated ink volume dispensed from a given inkjet printer.
Bubble point is a measurement of the largest effective pore size in a symmetrical membrane that has through-porosity, as measured according to ASTM F-316, and can range from about 0.20 xcexcm to about 2.0 xcexcm and preferably about 0.40 xcexcm to about 0.80 xcexcm.
Surface energy of the porous substrate before treating with the pigment and fluid management systems can range from 20 to 70 dynes/cm as defined in the Third Edition of the POLYMER HANDBOOK by J. Brandrup and E. H. Immergut (1989).
Microporous membranes can be of unlimited length, depending on the size of the roll that can be facilely handled. Usually, commercial quantities of the microporous membrane for feeding into a commercial printer can be a roll having a length in excess of 10 meters, and preferably in excess of 20 meters.
As inkjet media become more useful with wide format inkjet printers, the width of the microporous membrane becomes important from a perspective of imaging productivity and convenient graphic installation. The membrane can have a width ranging from about 0.25 meters to about 2 meters and preferably a width ranging from about 0.60 meters to about 1.2 meters.
More preferably, the inkjet receptor medium uses a Thermally Induced Phase Separated (T.I.P.S.) microporous membrane according the disclosures of U.S. Pat. Nos. 4,539,256 (Shipman et al.), 4,726,989 (Mrozinski), and more particularly 5,120,594 (Mrozinski), and available from 3M. For optimization, the pore size and pore volume of the porous film can be adjusted for the model or make of the ink jet printer to correctly hold the volume of ink dispensed by the printer ensuring the highest possible image quality. The coating on the preferred media/ink set has special utility in the demanding ink jet printing applications found in commercial printing. Thus, one can xe2x80x9cfine tunexe2x80x9d the properties of these receptors to deal with the variables of inkjet ink delivery, including without limitation: drop volume, porosity of media, and capacity of media to receive ink. Moreover, these media exhibit a complex porosity in its porous material that provides both a tortuous path for fluid management and a tortuous path that ensnares the pigment initially and continually during ink delivery.
Pigment Drying Agents
Pigment drying agents can be useful in the present invention and can comprise aromatic or aliphatic acids having sulfonic, carboxylic, phenolic or mixed functionalities thereof. Further information can be found in copending, coassigned, U.S. patent application Ser. No. 09/099,961, now U.S. Pat. No. 6,383,612.
Preferably, aromatic sulfonic and carboxylic acids have been found in this invention to be very effective in presence of multivalent metal salts and suitable surfactant and binder, to serve as drying agents for inkjet receptor media. These acids can be of various types, chosen according to properties and distinguished by extent of their solubility in water and how that solubility affects drying performance.
At one end of the range of candidate acids, their higher solubility in water can interfere with other components in the media, such as a migration inhibitor as disclosed in copending, coassigned, U.S. patent application Ser. No. 09/099,956, now U.S. Pat. No. 6,537,650, thereby perhaps requiring a greater concentration of drying agent to be included in the coating. One example of this type of acid is a sulfocarboxylic acid such as sulfosalicylic acid.
At the other end of the range of candidate acids, the candidate acids with lower solubility in water would perform the drying function excellently but could require more aggressive solvent(s) to be impregnated into the media. One example of this type of acid is a phthalic acid so long as it is recognized that impregnating the receptor media will be more challenging because of the acid""s lower solubility. To overcome impregnating limitations, lower solubility acid candidates, such as aromatic carboxylic acids, can be derivatized to become a monosodium salt (or any other similar alkali metal salt), the solubility of that salt in water is enhanced. One example of this type of acid-salt is an aromatic carboxylic acid, sodium salt such as ortho-phthalic acid-sodium salt. Furthermore, the aromatic carboxylic acids are also sufficiently soluble in water when the aromatic moiety contains at least one sulfonic acid group attached to the aromatic ring either as acid or as its sodium salt (or other alkali metal salts). Two examples of these candidates are 5-sulfoisophthalic acid and also its monosodium salt.
Other functional groups such asxe2x80x94OH group can be attached to the aromatic moiety to increase the solubility of the aromatic carboxylic group. Examples in this category are hydroxy-aryldicarboxylic acid isomers.
A related factor to choice of lower water solubility candidate acid is the amount of the acid to be included in the receptor media. The relationship is generally such that the lower solubility acid candidates are needed in smaller amounts than the higher solubility acid candidates. Generally, an acid used in the present invention can be present in the receptor medium in an amount ranging from about 1 to about 20 weight percent of the total coating weight of compositions with which the medium is impregnated with a fluid management system/pigment management system according to the disclosure of copending, coassigned, U.S. patent application Ser. No. 08/892,902 (Waller et al.), now U.S. Pat. No. 6,632,510, the disclosure of which is incorporated by reference herein. Preferably, the amount ranges from about 4 to about 15 weight percent. Thus, a sodium salt of an aromatic sulfocarboxylic acid should be present in an amount in the higher end of the range (e.g., about 15 weight percent), whereas a carboxylic acid should be present in an amount in the lower end of the range (e.g., about 5 weight percent).
Moreover, free acid and salt forms of that acid can be combined for controlled tailoring of impregnation processing and resulting drying performance.
The acid or its salt can be impregnated into the media by adding it to a coating solution otherwise being impregnated into the media for fluid management and pigment management purposes. Suitable coating solutions and impregnation techniques are disclosed in copending, coassigned, U.S. patent application Ser. No. 08/892,902, now U.S. Pat. No. 6,632,510, the disclosure of which is incorporated by reference herein for coating on the inkjet receptor medium. Typically, the coating solution comprises a multivalent 10 inorganic salt, a suitable surfactant, an alcohol and water. The weight percent of the acid/salt being used usually ranges from about 40 to about 60 weight percent and more preferably from about 45 to about 55 weight percent of the total solids in the composition.
Pigment Migration Inhibitors
Pigment migration inhibitors can be used in the present invention as an optional additive. These inhibitors can be homopolymers or copolymers having any number of hydrophilic monomers, each of whose homopolymers are hydrophilic, so long as the resulting copolymer is sparingly soluble in water. Pigment migration inhibitors are further disclosed in copending, coassigned, U.S. patent application Ser. No. 09/099,956, now U.S. Pat. No. 6,537,650, the disclosure of which is incorporated herein by reference.
Nonlimiting examples of hydrophilic monomers are methacrylic, ethacrylic acids, acrylic acid, N-Vinylphthalimide, Vinylimidazole, Vinylpyridine and N-vinyl-2-pyrrolidinone, with the last and acrylic acid being presently preferred. The homopolymer is a polyvinylpyrrolidinone (PVP) of relatively high molecular weight available from commercial sources.
Other ink receptive copolymers that are sparingly soluble in water include a copolymer of N-vinylpyrrolidone, acrylic acid, and trimethoxysilylethylmethacrylate (80/10/10); a copolymer of N-vinylpyrrolidone, acrylic acid, trimethoxysilylethylmethacrylate, and ethyleneoxide acrylate (75/10/5/10); a copolymer of N-vinylpyrrolidone, acrylic acid, and N, N, N-methyloctylheptadecafluorosulfonylethylacrylate (MeFOSEA) (80/10/10); a copolymer of N-vinylpyrrolidone, acrylic acid, trimethoxysilylethylmethacrylate and N, N, N-ethyloctylheptadecafluorosulfonylethylacrylate (MeFOSEA) (83/10/2/5); and, a copolymer of N-vinylpyrrolidone, acrylic acid, and Sulfonated Styrenexe2x80x94Sodium Salt (60/10/30).